1. Field of the Invention
One aspect of this invention concerns making tetrahydrofuran, 1,4-butanediol or mixtures thereof by hydrogenating a variety of hydrogenatable precursors such as maleic acid, maleic anhydride, fumaric acid, succinic acid, malic acid, dimethyl succinate, .gamma.-butyrolactone or mixtures thereof. These precursors can be described as dicarboxylic acids, dicarboxylic acid esters, lactones or mixtures of said acids, esteres, lactones and/or anhydrides. Another aspect of this invention concerns a continuous catalytic process for making tetrahydrofuran, 1,4-butanediol or mixtures thereof from a normal C.sub.4 hydrocarbon such as n-butane. The particular Pd/Re/C catalyst employed for these processes is another aspect of this invention as is the preferred method for making the catalyst.
2. State of the Art
There are numerous methods disclosed in the art for making tetrahydrofuran and 1,4-butanediol. There are publications relating to the hydrogenation of maleic acid or maleic anhydride that also describe various attempts to maximize product yields. For instance, in this regard see: U.S. Pat. No. 4,155,919, U.S. Pat. No. 3,957,827, U.S. Pat. No. 3,370,067 and U.S. Pat. No. 3,113,138; Japanese Patent Publications Nos. 32439/74 and 43683/69; German Patent Publications Nos. 2,519,817 and 2,715,667; and British Pat. No. 1,534,232. These publications describe catalytic processes for making maleic acid/maleic anhydride; U.S. Pat. No. 4,251,390, U.S. Pat. No. 4,231,943, U.S. Pat. No. 4,244,878 and U.S. Pat. No. 4,283,288.
French Pat. No. 2,505,819 discloses hydrogenation reactions employing supported Rd/Re catalysts. Although the catalysts can be made by sequential deposition of Pd and Re metal, no intermediate reduction is disclosed.
The subject of this invention concerns optimization of the process for making tetrahydrofuran and 1,4-butanediol. The described methods employ a selected catalyst to produce high yields of tetrahydrofuran and 1,4-butanediol with high productivity. The methods proceed from dicarboxylic acid or dicarboxylic acid ester starting reactants. The methods of this invention are characterized in that they can be oriented, as desired, toward production of high ratios of tetrahydrofuran to 1,4-butanediol or vice versa.